Production of a semiconductor device involves a step of forming an electroconductive film on the surface of a wafer to form a wiring layer by photolithography, etching etc., a step of forming an interlaminar insulating film on the wiring layer, etc., and an uneven surface made of an electroconductive material such as metal and an insulating material is generated on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring is advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique wherein while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry). As shown in FIG. 1, a polishing apparatus used generally in CMP is provided for example with a polishing platen 2 for supporting a polishing pad 1, a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4, a backing material for uniformly pressurizing a wafer, and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing platen 2 for example via a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7 respectively and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pushing the polished material 4 against the polishing pad 1.
Conventionally, such a polishing pad is manufactured by a batch method such as (1) a method including casting a resin material into a mold to form a resin block and slicing the resin block with a slicer, (2) a method including casting a resin material into a mold and pressing the resin material to form a thin sheet, or (3) a method including melting a raw resin material and extruding the melt from a T die to form a sheet directly.
A method of continuously producing a polyurethane-polyurea polishing sheet material is also proposed to prevent variations in hardness, cell size or the like, which would otherwise be caused by batch production methods (Patent Literature 1). Specifically, this method includes mixing raw materials for polyurethane, a fine powder with particle sizes of 300 μm or less, and an organic foaming agent, discharging and casting the mixture into the space between a pair of endless surface belts, then performing a polymerization reaction of the mixture using heating means, and separating the resulting sheet-shaped product from the surface belts so that a polishing sheet material is obtained.
When CMP is conducted, there is a problem of judging the planarity of wafer surface. That is, the point in time when desired surface properties or planar state are reached should be detected. With respect to the thickness of an oxide film, polishing speed etc., the polishing treatment of a test wafer has been conducted by periodically treating the wafer, and after the results are confirmed, a wafer serving as a product is subjected to polishing treatment.
In this method, however, the treatment time of a test wafer and the cost for the treatment are wasteful, and a test wafer and a product wafer not subjected to processing are different in polishing results due to a loading effect unique to CMP, and accurate prediction of processing results is difficult without actual processing of the product wafer.
Accordingly, there is need in recent years for a method capable of in situ detection of the point in time when desired surface properties and thickness are attained at the time of CMP processing, in order to solve the problem described above. While various methods are used for such detection, an optical detection method using a film thickness monitoring mechanism with a laser beam, which is incorporated in a rotary platen, is becoming the mainstream in view of measurement accuracy or spatial resolution in non-contact measurement (Patent Literatures 2 and 3).
The optical detection means is specifically a method of detecting the endpoint of polishing by irradiating a wafer via a polishing pad through a window (light-transmitting region) with a light beam, and monitoring an interference signal generated by reflection of the light beam.
In such method, the endpoint is determined by knowing an approximate depth of surface unevenness by monitoring a change in the thickness of a surface layer of a wafer. When such change in thickness becomes equal to the thickness of unevenness, the CMP process is finished. As a method of detecting the endpoint of polishing by such optical means and a polishing pad used in the method, various methods and polishing pads have been proposed.
A polishing pad having, as least a part thereof, a solid and uniform transparent polymer sheet passing a light of wavelengths of 190 to 3500 nm therethrough is disclosed (Patent Literature 4). Further, a polishing pad having a stepped transparent plug inserted into it is disclosed (Patent Literature 5). A polishing pad having a transparent plug on the same surface as a polishing surface is disclosed (Patent Literature 6).
Besides, a proposal is also offered for preventing a slurry from leaking out an interface (joint line) between a polishing region and a light-transmitting region (Patent Literatures 7 and 8). However, the techniques of Patent Literatures 7 and 8 have a problem in which the transparent sheet or the fluid-impermeable layer may be easily separated due to slurry infiltration during polishing, because it is bonded to the polishing layer with a double-sided tape.
There is also disclosed a method for manufacturing a polishing pad, which includes placing a rod or plug of a first resin in a liquid of a second resin, curing the second resin to prepare a formed product, and slicing the formed product to form a polishing pad having a light-transmitting region and a polishing region integrated together (Patent Literature 9). In this manufacturing method, the light-transmitting region and the polishing region are integrated with each other, so that slurry leak can be prevented to some extent.
In the case of the manufacturing method of Patent Literature 9, however, voids (pores) can be formed at the interface between the first and second resins in the process of placing a rod or plug of the first resin in a liquid of the second resin, so that a slurry may leak through the voids. In addition, the method of Patent Literature 9 cannot be used to produce a long polishing pad.
Patent Literature 1: JP-A 2004-169038
Patent Literature 2: U.S. Pat. No. 5,069,002
Patent Literature 3: U.S. Pat. No. 5,081,421
Patent Literature 4: JP-A National Publication (Laid-Open) No. 11-512977
Patent Literature 5: JP-A 9-7985
Patent Literature 6: JP-A 10-83977
Patent Literature 7: JP-A 2001-291686
Patent Literature 8: JP-A National Publication (Laid-Open) No. 2003-510826
Patent Literature 9: JP-A 2005-210143